It is known that display panels such as liquid crystal panels and organic EL panels exhibit display unevenness (luminance unevenness and color unevenness) due to variations in manufacturing. When each pixel of the display panel has R, G, and B subpixels, luminance unevenness occurs if the absolute brightness relationship differs between adjacent pixels even though the relative brightness relationship among R, G, and B in each pixel does not differ. Also, color unevenness occurs if the relative brightness relationship among R, G, and B in each pixel differs between adjacent pixels. Specifically, in organic EL panels, in which it is difficult to make the thickness of an organic compound layer in each pixel uniform, display unevenness is likely to occur due to uneven layer thicknesses and thus realizing a large screen size is difficult.
As a technique for improving the image quality of a display panel by reducing such display unevenness, Patent Literature 1, for example, discloses a luminance measurement method. In this method, all pixels (referred to as “picture element” in this patent literature) of the display panel are turned on, the pixels are imaged at a plurality of imaging points of a CCD camera (see FIG. 5 of this patent literature), and the luminance of the pixels is calculated on the basis of luminance data at the plurality of imaging points. Correction data for reducing display unevenness is generated using the calculated luminance of each pixel, and an input signal to the display panel is corrected according to this correction data, thereby enabling an improvement in image quality of the display panel.